The present invention relates generally to new polyols and to an improvement in the process for making polyols. More particularly, the invention is directed to mono-, di-, tri-, tetra, penta and hexa-methylols produced by reacting ketones with formaldehyde and/or formaldehyde generators or donors.
The reaction between formaldehyde and acetone has been well characterized. As early as 1911, U.S. Pat. No. 989,993 (F. Bayer & Co.) described the condensation of acetone and formaldehyde in the presence of dilute alkali to form methylol acetone: ##STR1##
Later, Dreyfuss and Drewitt increased product yield and decreased by-product formation by using aqueous solvent systems and by maintaining the pH in a range between 8.5 and 9.5. (U.S. Pat. No. 2,387,933; British Celanese LTD). The product was once again monomethylol acetone.
The preparation of dimethylol acetone is described in U.S. Pat. No. 1,955,060 (I.G. Farbenindustrie A.G.). Dimethylol acetone can occur in unsymmetrical or symmetrical isomers: ##STR2## Preparation of dimethylol acetone, in accordance with prior art techniques, involves reacting formaldehyde with acetone, using strong inorganic alkali catalysts to maintain the pH above 10.0.
The following mechanistic scheme is believed to describe the role of the strong alkali catalysts in the methylolation of acetone:
1. Abstraction of hydrogen atom from alpha carbon atom: ##STR3##
2. Reaction of carbanion with formaldehyde: ##STR4##
3. Regeneration of catalyst: ##STR5##
In theory, the above mechanism is repeatable to the extent of substituting up to three molecules of formaldehyde on each alpha carbon atom of acetone. However, the reaction conditions become more stringent as each additional hydrogen attached the the alpha carbon atom is replaced by a methylol group.
As indicated, the prior art technique has been to form methylol substituted acetone by and large from a reaction of the acetone carbanion with formaldehyde. Stronger alkali is required to form the carbanion as the alpha carbon atom becomes more highly substituted. Accordingly, only the mono-and di-methylol acetones are known in the prior art.